The present invention relates to a semiconductor laser light source unit used for a remote control unit, an optical transmission unit, a unit for high-speed optical communication, etc.
Conventionally, a GaAs LED (wavelength: 950 nm) is used as a light source for a remote controller. While the GaAs LED has a rise time of 1 .mu.sec, an AlGaAs LED (wavelength: 850 nm), which has come to be used as a light source for high-speed optical signal transmission, has a shorter rise time of 0.3 .mu.sec.
However, even the AlGaAs LED cannot be used to transmit a high-frequency signal of more than 1 MHz. That is, the infrared light of the AlGaAs LED cannot accommodate the spatial transmission of an audio-video signal and an optical signal for communication between computers, which signals should carry a large amount of information.
To accommodate such cases, a semiconductor laser, whose build up is faster than the above-mentioned infrared LEDs and which enables transmission of high-speed pulses, is now being given much attention. However, the divergence angle of a laser beam emitted from the semiconductor laser depends on the angle around its axis, and the beam cross-section is elliptical rather than circular. More specifically, the laser beam travels toward a light-receiving surface with its cross-section assuming an elliptical far field pattern (FFP) whose major-axis is perpendicular to the pn junction plane (hereinafter also called "chip junction plane") of a laser chip.
Therefore, the laser beam can be directed easily so as to properly illuminate a predetermined position in the major-axis direction of the elliptical pattern, but is hardly directed to the predetermined position in the minor-axis direction (i.e., the direction in parallel with the chip junction plane) in which direction the light intensity distribution is too narrow. For example, when a device including a semiconductor laser is installed, its positioning with respect to a light-receiving surface is very difficult. In particular, such positioning by manual handling is extremely difficult.
On the other hand, the angular half-width (full width at half maximum) of the light intensity distribution in the major-axis direction of the elliptical pattern (the cross-section perpendicular to the beam axis) varies over a wide range of 25.degree. to 45.degree.. As a result, a peripheral part of the laser beam cannot be utilized because its light intensity is too low. For example, if the half-width of the light intensity distribution is in the 350.degree.-45.degree. range, the peripheral part of the beam has too low intensity to be used in a remote controller.
As a countermeasure, the light output power of the semiconductor laser needs to be increased to compensate for the unusable peripheral part of the beam. However, there arises a problem that high-light-output semiconductor lasers are expensive and have large electric power consumption. They are not suitable specifically for a battery-driven, handy terminal.